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Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost–effective solution in concentrated solar power plants (CSP). Such a device is made up of a tank filled with a granular bed through which heat-transfer fluid circulates. However, in such devices, the thermal stresses may accumulate from cycle to another due to differential thermal dilatation between filler and tank walls, leading to plastic deformations in the tank shell and the failure of the tank might happen. This paper aims at studying the evolution of tank wall stresses over thermal cycles, taking into account both thermal and mechanical loads, with a numerical model based on the discrete element method (DEM). A higher thermal expansion coefficient is used for the wall compared to the granular medium, allowing the settlement of particles during the loading phases, then an increase of induced stresses during the unloading phases due to the wall contraction against the settled particles. Simulations were performed to study two different thermal configurations: (i) the tank is heated homogenously along its height or (ii) with a vertical gradient of temperature. Then, the resulting loading stresses applied on the tank are compared as well the response of the tank wall. [ABSTRACT FROM AUTHOR]

Thermocline energy storage is a way to store thermal energy by keeping two distinct zone of temperature in a tank, separated by a thin transition zone. Some applications use a granular porous media, filling the storage tank, through which passes the heat-transfer fluid. Most of scientific papers concerning this kind of technology assume that an ideal distribution of the fluid into the porous media is a homogeneous distribution over the diameter of the tank. On the other side, a recent numerical study concludes that a non-homogeneous distribution leads to better storage performances. Considering theses contradictory statements and the limited number of studies concerning the impact of distribution over thermal storage performances, a numerical simulation model is developed to investigate. This model is validated with data from the experimental device existing in CEA, in cases without distribution issues. Planned modifications of the experimental device for investigation of fluid’s distribution and validation of the model in such cases are presented. [ABSTRACT FROM AUTHOR]

Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost-effective solution in concentrated solar power plants (CSP). Such a device is made up of a tank filled with a granular bed through which heat-transfer fluid circulates. However, in such devices, the tank might be subjected to catastrophic failure induced by a mechanical phenomenon known as thermal ratcheting. Thermal stresses are accumulated during cycles of loading and unloading until the failure happens. This paper aims at studying the evolution of tank wall stresses over granular bed thermal cycles, taking into account both thermal and mechanical loads, with a numerical model based on the discrete element method (DEM). Simulations were performed to study two different thermal configurations: (i) the tank is heated homogenously along its height or (ii) with a vertical gradient of temperature. Then, the resulting loading stresses applied on the tank are compared as well the response of the internal granular material. [ABSTRACT FROM AUTHOR]

This work presents some of the experimental results obtained during a test campaign performed at the STONE facility of CEA-Grenoble in collaboration with CIEMAT-PSA supported by both the SFERA-II and the STAGE-STE project. This installation consists of a thermocline tank with thermal oil and rock/sand filler and the tests aimed to study the development of the temperature profile inside the tank at the beginning of charge/discharge processes. The investigation of how this profile is created and which is its dependence on the experimental parameters is crucial for predicting the behavior of a dual-media thermocline tank. Tests have been performed for dynamic processes from initial states with constant uniform temperature or with a thermal gradient already present due to a partial thermocline zone extraction in the former process. Tests at different fluid velocities and temperatures have been carried out as well, in order to evaluate the influence of operating conditions. When a dynamic process of charge or discharge is started, the development of the thermal front is very sharp and localized at tank top or bottom if initial tank temperature is uniform, whereas it is less pronounced if the test begins from a non-thermally uniform initial state. In terms of operating conditions, it has been observed that the development of the thermocline thermal front is independent not only of the fluid velocity but also of its temperatures, within the working ranges here considered. Due to these experimental results, it will be possible to improve simulation models for thermocline tanks and hence to predict their behavior more accurately, especially when they are implemented in annual simulations of CSP plants. [ABSTRACT FROM AUTHOR]